######################## BEGIN LICENSE BLOCK ########################
# The Original Code is mozilla.org code.
#
# The Initial Developer of the Original Code is
# Netscape Communications Corporation.
# Portions created by the Initial Developer are Copyright (C) 1998
# the Initial Developer. All Rights Reserved.
#
# Contributor(s):
#   Hui (zhengzhengzheng@gmail.com) - port to Ruby
#   Mark Pilgrim - first port to Python
#
# This library is free software; you can redistribute it and/or
# modify it under the terms of the GNU Lesser General Public
# License as published by the Free Software Foundation; either
# version 2.1 of the License, or (at your option) any later version.
# 
# This library is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
# Lesser General Public License for more details.
# 
# You should have received a copy of the GNU Lesser General Public
# License along with this library; if not, write to the Free Software
# Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
# 02110-1301  USA
######################### END LICENSE BLOCK #########################

require 'UniversalDetector'
require 'CharSetProber'

module  UniversalDetector
    # This prober doesn't actually recognize a language or a charset.
    # It is a helper prober for the use of the Hebrew model probers

    ### General ideas of the Hebrew charset recognition ###
    #
    # Four main charsets exist in Hebrew:
    # "ISO-8859-8" - Visual Hebrew
    # "windows-1255" - Logical Hebrew 
    # "ISO-8859-8-I" - Logical Hebrew
    # "x-mac-hebrew" - ?? Logical Hebrew ??
    #
    # Both "ISO" charsets use a completely identical set of code points, whereas
    # "windows-1255" and "x-mac-hebrew" are two different proper supersets of 
    # these code points. windows-1255 defines additional characters in the range
    # 0x80-0x9F as some misc punctuation marks as well as some Hebrew-specific 
    # diacritics and additional 'Yiddish' ligature letters in the range 0xc0-0xd6.
    # x-mac-hebrew defines similar additional code points but with a different 
    # mapping.
    #
    # As far as an average Hebrew text with no diacritics is concerned, all four 
    # charsets are identical with respect to code points. Meaning that for the 
    # main Hebrew alphabet, all four map the same values to all 27 Hebrew letters 
    # (including final letters).
    #
    # The dominant difference between these charsets is their directionality.
    # "Visual" directionality means that the text is ordered as if the renderer is
    # not aware of a BIDI rendering algorithm. The renderer sees the text and 
    # draws it from left to right. The text itself when ordered naturally is read 
    # backwards. A buffer of Visual Hebrew generally looks like so:
    # "[last word of first line spelled backwards] [whole line ordered backwards
    # and spelled backwards] [first word of first line spelled backwards] 
    # [end of line] [last word of second line] ... etc' "
    # adding punctuation marks, numbers and English text to visual text is
    # naturally also "visual" and from left to right.
    # 
    # "Logical" directionality means the text is ordered "naturally" according to
    # the order it is read. It is the responsibility of the renderer to display 
    # the text from right to left. A BIDI algorithm is used to place general 
    # punctuation marks, numbers and English text in the text.
    #
    # Texts in x-mac-hebrew are almost impossible to find on the Internet. From 
    # what little evidence I could find, it seems that its general directionality
    # is Logical.
    #
    # To sum up all of the above, the Hebrew probing mechanism knows about two
    # charsets:
    # Visual Hebrew - "ISO-8859-8" - backwards text - Words and sentences are
    #    backwards while line order is natural. For charset recognition purposes
    #    the line order is unimportant (In fact, for this implementation, even 
    #    word order is unimportant).
    # Logical Hebrew - "windows-1255" - normal, naturally ordered text.
    #
    # "ISO-8859-8-I" is a subset of windows-1255 and doesn't need to be 
    #    specifically identified.
    # "x-mac-hebrew" is also identified as windows-1255. A text in x-mac-hebrew
    #    that contain special punctuation marks or diacritics is displayed with
    #    some unconverted characters showing as question marks. This problem might
    #    be corrected using another model prober for x-mac-hebrew. Due to the fact
    #    that x-mac-hebrew texts are so rare, writing another model prober isn't 
    #    worth the effort and performance hit.
    #
    #### The Prober ####
    #
    # The prober is divided between two SBCharSetProbers and a HebrewProber,
    # all of which are managed, created, fed data, inquired and deleted by the
    # SBCSGroupProber. The two SBCharSetProbers identify that the text is in
    # fact some kind of Hebrew, Logical or Visual. The final decision about which
    # one is it is made by the HebrewProber by combining final-letter scores
    # with the scores of the two SBCharSetProbers to produce a final answer.
    #
    # The SBCSGroupProber is responsible for stripping the original text of HTML
    # tags, English characters, numbers, low-ASCII punctuation characters, spaces
    # and new lines. It reduces any sequence of such characters to a single space.
    # The buffer fed to each prober in the SBCS group prober is pure text in
    # high-ASCII.
    # The two SBCharSetProbers (model probers) share the same language model:
    # Win1255Model.
    # The first SBCharSetProber uses the model normally as any other
    # SBCharSetProber does, to recognize windows-1255, upon which this model was
    # built. The second SBCharSetProber is told to make the pair-of-letter
    # lookup in the language model backwards. This in practice exactly simulates
    # a visual Hebrew model using the windows-1255 logical Hebrew model.
    #
    # The HebrewProber is not using any language model. All it does is look for
    # final-letter evidence suggesting the text is either logical Hebrew or visual
    # Hebrew. Disjointed from the model probers, the results of the HebrewProber
    # alone are meaningless. HebrewProber always returns 0.00 as confidence
    # since it never identifies a charset by it@ Instead, the pointer to the
    # HebrewProber is passed to the model probers as a helper "Name Prober".
    # When the Group prober receives a positive identification from any prober,
    # it asks for the name of the charset identified. If the prober queried is a
    # Hebrew model prober, the model prober forwards the call to the
    # HebrewProber to make the final decision. In the HebrewProber, the
    # decision is made according to the final-letters scores maintained and Both
    # model probers scores. The answer is returned in the form of the name of the
    # charset identified, either "windows-1255" or "ISO-8859-8".

    # windows-1255 / ISO-8859-8 code points of interest
    FINAL_KAF = '\xea'
    NORMAL_KAF = '\xeb'
    FINAL_MEM = '\xed'
    NORMAL_MEM = '\xee'
    FINAL_NUN = '\xef'
    NORMAL_NUN = '\xf0'
    FINAL_PE = '\xf3'
    NORMAL_PE = '\xf4'
    FINAL_TSADI = '\xf5'
    NORMAL_TSADI = '\xf6'

    # Minimum Visual vs Logical final letter score difference.
    # If the difference is below this, don't rely solely on the final letter score distance.
    MIN_FINAL_CHAR_DISTANCE = 5

    # Minimum Visual vs Logical model score difference.
    # If the difference is below this, don't rely at all on the model score distance.
    MIN_MODEL_DISTANCE = 0.01

    VISUAL_HEBREW_NAME = "ISO-8859-8"
    LOGICAL_HEBREW_NAME = "windows-1255"

    class HebrewProber < CharSetProber
        def initialize
            super
            @_mLogicalProber = nil
            @_mVisualProber = nil
            reset()
        end

        def reset
            @_mFinalCharLogicalScore = 0
            @_mFinalCharVisualScore = 0
            # The two last characters seen in the previous buffer,
            # mPrev and mBeforePrev are initialized to space in order to simulate a word 
            # delimiter at the beginning of the data
            @_mPrev = ' '
            @_mBeforePrev = ' '
            # These probers are owned by the group prober.
        end

        def set_model_probers(logicalProber, visualProber)
            @_mLogicalProber = logicalProber
            @_mVisualProber = visualProber
        end

        def is_final(c)
            return [FINAL_KAF, FINAL_MEM, FINAL_NUN, FINAL_PE, FINAL_TSADI].include?(c)
        end

        def is_non_final(c)
            # The normal Tsadi is not a good Non-Final letter due to words like 
            # 'lechotet' (to chat) containing an apostrophe after the tsadi. This 
            # apostrophe is converted to a space in FilterWithoutEnglishLetters causing 
            # the Non-Final tsadi to appear at an end of a word even though this is not 
            # the case in the original text.
            # The letters Pe and Kaf rarely display a related behavior of not being a 
            # good Non-Final letter. Words like 'Pop', 'Winamp' and 'Mubarak' for 
            # example legally end with a Non-Final Pe or Kaf. However, the benefit of 
            # these letters as Non-Final letters outweighs the damage since these words 
            # are quite rare.
            return [NORMAL_KAF, NORMAL_MEM, NORMAL_NUN, NORMAL_PE].include?(c)
        end

        def feed(aBuf)
            # Final letter analysis for logical-visual decision.
            # Look for evidence that the received buffer is either logical Hebrew or 
            # visual Hebrew.
            # The following cases are checked:
            # 1) A word longer than 1 letter, ending with a final letter. This is an 
            #    indication that the text is laid out "naturally" since the final letter 
            #    really appears at the end. +1 for logical score.
            # 2) A word longer than 1 letter, ending with a Non-Final letter. In normal
            #    Hebrew, words ending with Kaf, Mem, Nun, Pe or Tsadi, should not end with
            #    the Non-Final form of that letter. Exceptions to this rule are mentioned
            #    above in isNonFinal(). This is an indication that the text is laid out
            #    backwards. +1 for visual score
            # 3) A word longer than 1 letter, starting with a final letter. Final letters 
            #    should not appear at the beginning of a word. This is an indication that 
            #    the text is laid out backwards. +1 for visual score.
            # 
            # The visual score and logical score are accumulated throughout the text and 
            # are finally checked against each other in GetCharSetName().
            # No checking for final letters in the middle of words is done since that case
            # is not an indication for either Logical or Visual text.
            # 
            # We automatically filter out all 7-bit characters (replace them with spaces)
            # so the word boundary detection works properly. [MAP]

            if get_state() == :NotMe
                # Both model probers say it's not them. No reason to continue.
                return :NotMe
            end

            aBuf = filter_high_bit_only(aBuf)

            aBuf.each_char do |cur|
                if cur == ' '
                    # We stand on a space - a word just ended
                    if @_mBeforePrev != ' '
                        # next-to-last char was not a space so @_mPrev is not a 1 letter word
                        if is_final(@_mPrev)
                            # case (1) [-2:not space][-1:final letter][cur:space]
                            @_mFinalCharLogicalScore += 1
                        elsif is_non_final(@_mPrev)
                            # case (2) [-2:not space][-1:Non-Final letter][cur:space]
                            @_mFinalCharVisualScore += 1
                        end
                    end
                else
                    # Not standing on a space
                    if (@_mBeforePrev == ' ') and (is_final(@_mPrev)) and (cur != ' ')
                        # case (3) [-2:space][-1:final letter][cur:not space]
                        @_mFinalCharVisualScore += 1
                    end
                end
                @_mBeforePrev = @_mPrev
                @_mPrev = cur
            end

            # Forever detecting, till the end or until both model probers return eNotMe (handled above)
            return :Detecting
        end

        def get_charset_name
            # Make the decision: is it Logical or Visual?
            # If the final letter score distance is dominant enough, rely on it.
            finalsub = @_mFinalCharLogicalScore - @_mFinalCharVisualScore
            if finalsub >= MIN_FINAL_CHAR_DISTANCE
                return LOGICAL_HEBREW_NAME
            end
            if finalsub <= -MIN_FINAL_CHAR_DISTANCE
                return VISUAL_HEBREW_NAME
            end

            # It's not dominant enough, try to rely on the model scores instead.
            modelsub = @_mLogicalProber.get_confidence() - @_mVisualProber.get_confidence()
            if modelsub > MIN_MODEL_DISTANCE
                return LOGICAL_HEBREW_NAME
            end
            if modelsub < -MIN_MODEL_DISTANCE
                return VISUAL_HEBREW_NAME
            end

            # Still no good, back to final letter distance, maybe it'll save the day.
            if finalsub < 0.0
                return VISUAL_HEBREW_NAME
            end

            # (finalsub > 0 - Logical) or (don't know what to do) default to Logical.
            return LOGICAL_HEBREW_NAME
        end

        def get_state
            # Remain active as long as any of the model probers are active.
            if (@_mLogicalProber.get_state() == :NotMe) and (@_mVisualProber.get_state() == :NotMe)
                return :NotMe
            end
            return :Detecting
        end
    end
end
